Three cases of rare low-grade endometrial stromal sarcoma of the extrauterine tissue are presented. Each one occurred in the ovary, pelvic and abdominal cavities. Two were associated with endometriosis. Histologically, the tumors were characterized by an infiltrative and diffuse proliferation of uniform round or oval cells, abundant small vessels, low mitotic activity, the presence of foam cells and vascular invasion. Immunohistochemically, all tumors expressed vimentin, muscle markers (desmin, muscle-specific actin and α-smooth muscle actin) and progesterone receptors. Two tumors were diploid and one was aneuploid by flow cytometry. All patients were well with no evidence of disease 16-39 months after surgery. It is suggested that this neoplasm may arise with or without endometriosis under hormonal influence. This rare variant of Müllerian tumors should not be confused with adenosarcoma and soft tissue tumors, such as smooth muscle tumors and solitary fibrous tumor.